True or False: Fuel oil begins to come apart when subject to a vacuum in excess of 10".

Fuel oil does indeed begin to undergo changes when subjected to a vacuum exceeding 10 inches of mercury. This is primarily due to the fact that high levels of vacuum can lead to cavitation and the boiling of lighter fractions within the fuel oil composition, which can affect its stability and performance.

When the pressure drops significantly, as it does in a vacuum situation, the fuel oil can experience a breakdown or separation of its components. This can lead to the formation of sludge or other byproducts that might compromise the oil's integrity and make it less efficient for combustion processes. Maintaining appropriate vacuum levels is critical in systems that utilize fuel oil to ensure optimal combustion and prevent any adverse effects on the fuel quality.